The structure of the glycan of human thrombin has been determined, and the functional significance of this moiety has been sought. Enzymatic removal of the terminal mono-, di- and trisaccharides of the carbolydrate chain does not alter thrombin's ability to clot fibrinogen, to stimulate and aggregate platelets, to activate factor VIII:C, to bind to fibrin, or to be inhibited by anti-thrombin III or alpha 2-macroglobulin.